Recently, in a semiconductor device manufacturing method, a case where a multilayer film is collectively processed for QTAT (Quick Turnaround Time) is increased. More particularly, in an etching process using plasma as in RIE (Reactive Ion Etching) process, a case where a multilayer film is collectively processed in a continuous process is increased. In the collective process of the multilayer film, a continuous process is performed by sequentially and continuously switching proper process conditions such as a gas flow rate, a pressure, a temperature, and a power for each layer to be processed while maintaining plasma discharge.
In the continuous process, since an impedance value of plasma is varied and a plasma state becomes unstable when the respective process conditions are switched, according to an ordinary method, a next process is performed after a matching circuit interposed between a power supply and a plasma processing device matches impedances to stabilize plasma. In the ordinary method, there is a tendency that a long time is consumed until the impedances are matched.
In contrast, there is also proposed a method of matching impedances using a matching value corresponding to process conditions before switching and a matching value corresponding to process conditions after switching. In this method, there is a tendency that since an impedance matching value is prone to be switched before a gas flow rate and a pressure are stabilized impedances are difficult to be matched and plasma can easily disappear, and even when impedances are matched a long time is necessary until plasma is stabilized. Accordingly, it is necessary to secure long time for switching an impedance after a gas flow rate and a pressure are stabilized.